<p></p>
<p>Bill Henderson</p>
<div class="gmail_quote">On Oct 3, 2011 12:56 PM, "Ronald Van Putte" <<a href="mailto:vanputte@cox.net">vanputte@cox.net</a>> wrote:<br type="attribution">> I was afraid that would be the case. I am well aware of the airplane <br>
> requirements regarding power required for various "missions". It's <br>> just that I was not sure that the two ESCs would work together, due <br>> to the feedback from the motor to the ESC.<br>
> <br>> We'd have tried an E prop with less pitch or smaller diameter or <br>> both, but didn't have the right props with us.<br>> <br>> Thanks for the input.<br>> <br>> Ron<br>> <br>> <br>
> <br>> On Oct 3, 2011, at 9:38 AM, Peter Vogel wrote:<br>> <br>>> Hi Ron,<br>>><br>>> I don't think you can Y the motor connections that way, the ESC's <br>>> are putting out pulses very specifically timed to move the motor <br>
>> through to the next set of poles and rotate it in the correct <br>>> direction while one of the three leads (and it changes for each <br>>> phase of the rotation) is used to sense the position of the motor <br>
>> to time the next magnetic pulse. Unless the ESC's are in *perfect* <br>>> sync they will wind up fighting each other and could even <br>>> misinterpret the pulses from the other ESC as a timing pulse from <br>
>> the motor.<br>>><br>>> There are no shortcuts to a proper electric power system. Prop, <br>>> Motor, ESC + Batteries should be chosen to deliver the right amount <br>>> of power (Watts) + thrust to fly the airplane for the mission <br>
>> intended (70 watts/lb of all up weight for a trainer, 200 watts/lb <br>>> for aerobatic sport flying, 300 watts/lb for 3D -- as a general <br>>> rule of thumb). Most motor manufacturers will publish prop charts <br>
>> showing the amp draw on the intended voltage for the motor, you <br>>> should look for a prop that will not overtax the motor/ESC combo on <br>>> the voltage you are planning to use.<br>>><br>
>> Remember that an electric power system is a *constant speed* <br>>> system, as opposed to an internal combustion system which is <br>>> constant power. What that means is that the motor has a rated kV, <br>
>> the rotations per minute per volt and whatever load you put on the <br>>> motor (prop) the motor will try to spin at that speed and pull as <br>>> many amps as it needs in order to do that. Also remember that if <br>
>> you are measuring watts on the ground holding the plane, that's a <br>>> static measurement and the load should drop somewhat when the prop <br>>> is allowed to pull the plane through the air, reducing the <br>
>> current. Adding volts to the same motor (i.e. going to 6s <br>>> batteries) doesn't necessarily help because that motor's kV is the <br>>> same, it may, in fact, make things worse. If you want to go to 6s, <br>
>> you need to get a motor with a different wind to reduce the kV so <br>>> that you are getting the same RPM as you did at 5s with the other <br>>> motor. THEN you will reduce amp draw by about 20% because you <br>
>> increased voltage by about 20% and you are still delivering the <br>>> same watts.<br>>><br>>> If he's running 71 watts in a static test at wide open throttle, <br>>> I'd consider reducing the diameter of the prop by 1 inch or <br>
>> reducing the pitch of the prop by 1 inch, that should get him into <br>>> a reasonable range for a 60 amp ESC (though I prefer about a 20% <br>>> headroom -- check the amps at WOT after propping down and if it's <br>
>> at or near 60 the unload in real flight should give you about 10% <br>>> headroom).<br>>><br>>> Peter+<br>>><br>>> On Mon, Oct 3, 2011 at 7:19 AM, Ronald Van Putte <<a href="mailto:vanputte@cox.net">vanputte@cox.net</a>> <br>
>> wrote:<br>>> I have an off-the-wall question that I don't have the answer to. <br>>> Somebody please tell me the answer.<br>>><br>>> A young local modeler has an electric-powered airplane whose motor <br>
>> puts out 1200 watts. He has 5S lipo batteries that will handle the <br>>> load. In a ground test, the maximum current was 71 amps, He had <br>>> tried a 45 amp and a 60 amp ESC and they failed. Hence the reason <br>
>> for the ground test and confirmation that he needed an ESC with a <br>>> higher amp capacity.<br>>><br>>> I went looking at BP Hobbies for one of their inexpensive BP ESCs <br>>> with an 80 amp capacity and they no longer sell them. Other high <br>
>> amp ESCs are $100+<br>>><br>>> Here's the question: Can he put two 40 watt ESCs in parallel? <br>>> Both would go to the throttle channel via a Y-adapter and the motor <br>>> connections would be similarly Yed together.<br>
>><br>>> I was also thinking of having him use a 6S battery pack and limit <br>>> the throttle to 60 amps, but I'm not sure he has the room for the <br>>> battery pack.<br>>><br>>> Ron Van Putte<br>
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